Obesity (i.e., excess energy intake and inadequate physical inactivity) is associated with increased risk of breast cancer among postmenopausal women. Effective and practical intervention strategies are needed to address the high prevalence of excess weight and sedentary lifestyle in middle-aged and older US women. Although web-based interventions to promote a healthy lifestyle are common, no studies have tested the use of web-integrated physical activity meters for promoting behavior change in this population. By leveraging innovative technology-based approaches, researchers and physicians may be able to replace intensive physical activity interventions with low-cost alternatives. OBJECTIVE: To test the feasibility of using a web- based self-monitoring technology (the FitBit) to promote physical activity among women at elevated risk for breast cancer (i.e., overweight/obese, inactive postmenopausal women). SPECIFIC AIMS: This pilot study proposes to use a 16-week randomized controlled trial of a novel intervention (FitBit activity monitor + training) vs. a pedometer to address the following aims: Primary aim: To investigate the effect of the FitBit-based intervention vs. provision of a pedometer on objective measures of physical activity and sedentary behavior. Secondary aim: To examine the acceptability and usage patterns of the device and website. METHODS: Fifty participants will be randomly assigned to receive (a) a FitBit monitor and training on use of the website or (b) a pedometer. The FitBit is a tiny physical activity tracking device that pairs with a website, wirelessly uploading activity data to provide the user with an easy-to-understand visualization of her daily activity patterns. Goal-setting features are used alongside simple graphs and charts to enhance self-monitoring of energy balance. Participants will be given a physical activity goal, trained in the use of the self-monitoring website, and asked to wear the FitBit clipped to their clothing every day for 16 weeks. The primary outcome will be change in MET-hours/day of physical activity, as measured by the ActiGraph GT3X accelerometer prior to randomization and at 16 weeks. Although this is a pilot study, we will have 80% power to observe an effect size of 0.7 at a significance level of p<0.10. Questionnaires will be used to measure intervention acceptability and direct data downloads will provide an objective assessment of usage patterns. CANCER RELEVANCE: Promotion of weight management and physical activity is an important aspect of breast cancer prevention because excess adiposity is associated with increased risk of post-menopausal breast cancer. As intervention research evolves, technology offers the potential for cancer prevention researchers to move away from costly traditional interventions toward easily disseminated interventions that can continue after the study has ended.